a) PGLS regression between the aggregate copy number of genes in set “negative regulation of transforming growth factor beta production” and rate of malignancy across mammals. b) Ancestral trait reconstruction of the aggregate gene count for the gene set “negative regulation of transforming growth factor beta production” (log transformed) and malignancy rate. Color scale shows the estimated evolutionary history of each trait, inferred using contMap function in the R package PhyTools (v2.1-1) (Revell 2012).